GMRS Radio Gremlin

[KwoodKing]

Howdy,
I apologize for the long read.
I’m writing today as a last ditch effort to solve a problem seeming to palgue me alone.
I installed a Midland MXT275 about six months ago, and have yet to use it. Not because I haven’t had anybody to talk with, but because it hasn’t worked one day.
NOAA transmissions come in crystal clear on the mobile radio while the my midland handheld struggles. The interesting part is when I am driving, transmissions from one handheld driving a little ways ahead of me sounds super garbled and unintelligible, but the handheld I have in the Jeep sounds perfectly fine…
Additionally, when I turn on the radio in the jeep while the vehicle is off, monitoring any channel is as clear as it gets. But as soon as I so much as even open a door (which turns the computer on I guess), the mobile radio shows two little lines which means it’s picking up more signal than it’s programmed base line minimum we would call zero. It goes away when the computer turns completely off again. You can hear alternator or spark plug whine when the engine is running and it’s receiving any transmission, but as soon as I start driving it’s all gone. Range stationary is no better than half a mile. I swear I know how to not break stuff, but maybe I’m lying to myself. I have one antenna cable ran to the swing gate in the rear following existing wiring and another cable ran underneath the dashboard and steering wheel to the driver side cowl. The only time the cable is outside the cab is when it exits at the cowl. I’ll attach a pic of that. I also have a video of when the handheld picks up that interference and another of the monitoring sound when the computer turns off. If there is anything for me to do I’ll do it. I don’t think it’s an SWR issue because the antennas pre-tuned and the same issue persists on the dinky little magnetic antenna that came with it. The radio is hardwired to the battery’s positive and it’s own frame ground. The antenna itself isn’t grounded to the frame but I have done that and it does not effect the stationary or driving interference. However, interestingly enough, when I hold the base of the antenna with my hand while it’s on the Jeep, the extra static goes away…
I’m lost. We’ve been through two radios and two antennas and two cables. What’s next? Two Jeeps? ?

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[roaniecowpony]

Someone way smarter than me will chime in. But I'd start isolating/testing things.

I'd get some coax and temporarily run to the antenna completely away from any wire bundle.

If the above doesn't help, I'd do the same with the power supply to the radio and also ensure I had an isolated ground (nothing else on that ground run to the chassis).

If the radio calls for an inline filter, change it out with a different one.

And that's about the extent of my guessing.

 

[lifeguard17cp]

To me this sounds like you have a bad feed line. Like what roaniecowpony I would try the radio with a different antenna. There is a chance that somewhere along the line (even at the manufacturer the braid and center conductor are touching.

 

[KwoodKing]

Thank you guys for the suggestions!
I’ve tried what both of you said about taking the antenna away from any wire bundles. I’ve moved the radio entirely.
To your point, the ground isn’t isolated I don’t think because, well, everything grounds to the frame but it’s on its own stud in the engine bay. I have not gotten the chance to try it on an external battery but I don’t think it’s a power feed problem (for the extra static; The engine whine most certainly is but that’s something to solve later on) because it goes away when I disconnect the coax from the radio. I just realized I should have tried disconnecting the antenna from the co-ax and leave that plugged in to the unit so I’ll try that tomorrow and report my findings. If I can get my brother to cooperate I’ll also try to get a video of the garbled sound while driving for anyone’s reference.

 

[KwoodKing]

I’ll drag out the multimeter to see if there’s a short in the cable, antenna, or radio just to have that stat.

 

[TheBirdie72]

Radio gremlin, you say…??

Yeah… you got a problem!

 

[KwoodKing]

Radio gremlin, you say…??

Yeah… you got a problem!

I was hoping somebody would make the connection!!

 

[jav_eee]

The general rule is to make your negative lead as short as possible and ground it to the nearest body ground from the radio body. Some people even go so far as grounding the radio body itself to that same spot.

Make sure your antenna mount is grounded/bonded to the body.

SWR, while set from the factory, will always be affected by the host vehicle. Especially when mounted in the spot you chose. You should check the SWR.

 

[KwoodKing]

Checked with the multimeter, no shorts whatsoever. Ground is solid from antenna base to radio negative wire so that’s not the problem. The interference goes away when I remove the antenna so maybe new development?

 

[KwoodKing]

The general rule is to make your negative lead as short as possible and ground it to the nearest body ground from the radio body. Some people even go so far as grounding the radio body itself to that same spot.

Make sure your antenna mount is grounded/bonded to the body.

SWR, while set from the factory, will always be affected by the host vehicle. Especially when mounted in the spot you chose. You should check the SWR.

Should I isolate the antenna ground (remove it from the radio) and run it shorter to the engine bay? Or perhaps move the antenna ground to the same spot as the radio ground?

 

[jav_eee]

Checked with the multimeter, no shorts whatsoever. Ground is solid from antenna base to radio negative wire so that’s not the problem. The i tercentenary goes away when I remove the antenna so maybe new development?

well the antenna will ground the body which will show ground on the negative wire. So you’d want to make sure there’s a good ground from the antenna mount to the body of the jeep with the negative wire disconnected. As long as there’s ground you’re good there. My next step would be to shorten the negative wire and ground it to the closest bolt to the radio body.

 

[ROK HEMI]

The fact that the radio performs well in key off situations and poorly with key on situations makes me think that there is not a problem with the antenna, SWR or shorting of the wiring. I would most likely think it is coming from EMI interference through most likely the radio power or grounding wiring as your coaxial antenna cable is shielded. As previously stated I would make the radio ground as short as possible and the antenna ground as short as possible which means they will not be connected together. Try that and see what happens, next step to me would be too get power as close to the radio as possible and not run it by any EMI generators like fan motors, radios, ignition systems, onboard computers etc.

Anxious to hear how this one is solved

 

[Walker Texas Wrangler]

I can't answer your problem, but I'm in the Kingwood area too and use a handheld (BTECH GMRS Pro). Let me know if you need me to transmit to you when you are testing...WRVQ987

BTW: I'm in Pinehurst (Atas) and have a hard time getting good signal with the repeaters. We're about mid to Conroe and Memorial, it's not the best spot.

 

[KwoodKing]

I can't answer your problem, but I'm in the Kingwood area too and use a handheld (BTECH GMRS Pro). Let me know if you need me to transmit to you when you are testing...WRVQ987

BTW: I'm in Pinehurst (Atas) and have a hard time getting good signal with the repeaters. We're about mid to Conroe and Memorial, it's not the best spot.

Oh that’s sweet, thanks! I get all kinds of transmissions off repeaters at least as far as New Orleans. I’ll definitely reach out to test whenever I’m more confident I wouldn’t waste your time.

 

[KwoodKing]

I'd get some coax and temporarily run to the antenna completely away from any wire bundle.

I used the little dinky antenna today and had that run far away from the vehicle while the radio itself was sitting in the passenger seat. No interference.
I used the little antenna as a probe and noticed it's the worst on the driver's side of the vehicle and in front. The signal is amplified by the 6dB antenna more so than the little one that came with the radio. I have another mount pre-wired to the back of the Jeep on the swing gate. I had avoided using it because I figured the fiberglass wasn't good for range in front of the vehicle. I was doing some research today to that old jeeps were built with grounding tabs between the hood and frame to keep RF inside the engine bay. Not surprisingly, the JL's hood is not grounded nor is the firewall so anything and everything radio waves get out. Now I'm curious if the interference from the engine bay hiders my RX/TX frontwards.

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